Ethernet (registered trademark) is a communication standard widely used in a computer network (LAN: Local Area Network) of a small scale area such as a network built within a same building. Recently, in order to reduce the network operation cost and the like, there is presented a type of network in which functions regarding network remote surveillance are added to Ethernet for expanding Ethernet to be used for WAN (Wide Area Network) which is a larger scale network. This is called Ethernet OAM (Operations, Administrations, Maintenance).
The Ethernet OAM is standardized as Y.1731 by ITU-T (International Telecommunication Union Telecommunication Standardization Sector) in 2006. Non-Patent Document 1 is the document of the standardization of Y.1731. Further, IEEE (the Institute of Electrical and Electronics Engineers, Inc.) also standardized it as IEEE 802.1ag in 2007.
In Non-Patent Document 1, a single end LM (Loss Measurement) protocol that is one of protocols used in the network remote surveillance is defined. The single end LM is a two-way protocol (bidirectional) with which a transmission device of one end transmits a message and a transmission device on another end upon receiving it returns a massage.
In the single end LM protocol, a part of the data packet transmission path on the network is defined as a maintenance section called MEG (Maintenance Entity Group), and the end point of the maintenance section is defined as MEP (Maintenance Entity Group End Point). Then, through transmitting and receiving OAM frames between the defined MEPs, the network remote surveillance functions such as failure surveillance, performance measurement, and protection switching are achieved.
With the single end LM protocol depicted in Non-Patent Document 1, the packet loss ratio that is the data packet loss generation ratio between MEPs is calculated by exchanging the transmission/reception numbers of user frames between MEPs that are the both ends of the maintenance section (MEG). Hereinafter, calculation of the packet loss ratio will be described.
FIG. 6 is an explanatory chart showing the structure of a transmission network 901 that is the target of the packet loss ratio calculation by the single end LM protocol depicted in Non-Patent Document 1. The transmission network 901 is constituted by connecting a plurality of transmission devices 910a, 910b,—(referred to as the transmission devices 910 as a general term hereinafter) disposed on a transmission path 930 for relaying communication OAM frames via the transmission path 930 and an operation management device 920 which executes operation managements of those transmission devices 910.
Note here that the four transmission devices 910a to d are disposed on the transmission path 930. A point-to-point transmission network (MEG: Maintenance Entity Group) is constituted by having the transmission devices 910a and 910d among those as both end points (MEP: Maintenance Entity Group End Point) and the transmission 910b and 910c as the relay points. Further, transmission from the transmission device 910a to 910d is referred to as the forward direction, and transmission from the transmission device 910d to 910a is referred to as the reverse direction.
FIG. 7 is an explanatory chart showing the actions for measuring the packet loss ratio between the transmission devices 910a and 910d on the transmission path 930 shown in FIG. 6. First, a first LMM frame including a latest transmission counter value TxFCf (a1) of the device itself is transmitted from the transmission device 910a to the transmission device 910d (step S950a).
The transmission device 910d upon receiving the first LMM frame adds a latest reception counter value RxFCf (d1) of the device itself within the first LMM frame (step S950a), generates a first LMR frame as a response for the first LMM frame, adds a latest transmission counter value TxFCb (d1) of the device itself thereto, and transmits it to the transmission device 910a (step S951d).
The transmission device 910a upon receiving the first LMR frame refers to the latest reception counter value RxFCb (a1) (step S951a). Then, the transmission device 910a transmits a second LMM frame after a predetermined waiting time (100 msec, for example) has passed from the transmission of the first LMM frame (step S952a). The second LMM frame contains a transmission counter value TxFCf (a2).
As in steps S950d and 951d described above, the transmission device 910d upon receiving the second LMM frame adds a latest reception counter value RxFCf (d2) to the received second LMM frame (step 952d), generates a second LMR frame that is the response for the second LMM frame, adds a latest transmission counter value TxFCb (d2) of the device itself, and transmits it to the transmission device 910a (step S953d).
The transmission device 910a upon receiving the second LMR frame refers to the latest reception counter value RxFCb (a2) (step S953a), and calculates the frame loss number by following Expression 1. Note, however, that ∥ shows that it is an arithmetic operation between modulo 32 (32-bit integer with no signs). For example, |0x000000001−0xFFFFFFFF|=2.
                    ⁢          (              Expression        ⁢                                  ⁢        1            )                  Forward      ⁢                          ⁢      direction      ⁢                          ⁢      frame      ⁢                          ⁢      transmission      ⁢                          ⁢      number        =                                  TxFCf          ⁡                      (                          a              ⁢                                                          ⁢              2                        )                          -                  TxFCf          ⁡                      (                          a              ⁢                                                          ⁢              1                        )                                                Forward      ⁢                          ⁢      direction      ⁢                          ⁢      frame      ⁢                          ⁢      loss      ⁢                          ⁢      number        =                                                TxFCf            ⁡                          (                              a                ⁢                                                                  ⁢                2                            )                                -                      TxFCf            ⁡                          (                              a                ⁢                                                                  ⁢                1                            )                                                  -                                            RxFCf            ⁡                          (                              d                ⁢                                                                  ⁢                2                            )                                -                      RxFCf            ⁡                          (                              d                ⁢                                                                  ⁢                1                            )                                                              Reverse      ⁢                          ⁢      direction      ⁢                          ⁢      frame      ⁢                          ⁢      transmission      ⁢                          ⁢      number        =                                  TxFCb          ⁡                      (                          d              ⁢                                                          ⁢              2                        )                          -                  TxFCb          ⁡                      (                          d              ⁢                                                          ⁢              1                        )                                                Reverse      ⁢                          ⁢      direction      ⁢                          ⁢      frame      ⁢                          ⁢      loss      ⁢                          ⁢      number        =                                                TxFCb            ⁡                          (                              d                ⁢                                                                  ⁢                2                            )                                -                      TxFCb            ⁡                          (                              d                ⁢                                                                  ⁢                1                            )                                                  -                                            RxFCb            ⁡                          (                              a                ⁢                                                                  ⁢                2                            )                                -                      RxFCb            ⁡                          (                              a                ⁢                                                                  ⁢                1                            )                                                  Thereby, frame loss number frame transmission number, i.e., the packet loss ratio, in both directions can be calculated with MEGs constituted between the transmission devices 910a and 910d that are MEPs.
Relating to that, there are following technical documents, for example. Among those, depicted in Patent Document 1 is a frame loss measurement method which, when a relay device receives an OAM frame, identifies the frame transmission/reception number in each section by writing the frame counter value of that device into the OAM frame and relaying it. Depicted in Patent Document 2 is a packet loss measurement system which collects flows constituting the traffic on a network, counts the flows from the start of a measurement, and calculates the packet loss ratio from the flow information of a same account.
Depicted in Patent Document 3 is a packet loss ratio calculation system which adds a transmission counter and a reception counter to quality measurement packets on both probes of the transmission side and the reception side and transmits/receives those to calculate the packet loss ratio of the outward and inward paths thereby. Depicted in Patent Document 4 is a monitoring method which compares BROAM cells transmitted/received mutually between the end points of a network and specifies the performance deteriorated section.    Patent Document 1: Japanese Unexamined Patent Publication 2008-244870    Patent Document 2: Japanese Unexamined Patent Publication 2002-152266    Patent Document 3: Japanese Unexamined Patent Publication 2008-085906    Patent Document 4: Japanese Unexamined Patent Publication Hei 09-200228
Non-Patent Document 1: “ITU-T Recommendation Y. 1731-OAM functions and mechanisms for Ethernet based networks”, Jan. 31, 2006, International Telecommunication Union (ITU), (Searched on May 20, 2011), Internet<URL: http://www.itu.int/itudoc/itu-t/aap/sg13aap/recaap/y1731/>
Loss of the data packet stops the communication on the network or causes a great deterioration in the communication speed and the communication quality, so that the packet loss ratio needs to be suppressed to a specific numerical value or less. In order to do so, it is necessary to quickly specify the occurrence point of a failure (e.g., cut in the optical fiber, fault generated in the transmission device, or the like) which may cause the packet loss on the transmission path.
However, the method of the single end LM protocol depicted in Non-Patent Document 1 shown in FIG. 6 and FIG. 7 can only measure the packet loss ratio in MEG by having transmission devices at specific two points on the transmission path as MEPs and taking those MEPs as both ends.
FIG. 8 is an explanatory chart showing the method for specifying a fault occurrence point, which is the packet loss ratio measurement method depicted in Non-Patent Document 1 shown in FIG. 6 and FIG. 7. For example, in a case where a high packet loss ratio is measured by having the transmission devices 910a to 910d as MEG (end-end surveillance section), it is necessary to designate more fractionated sections (segment surveillance sections) such as the segments between the transmission devices 910a to 910b, between 910b to 910c, and the like as MEG for specifying the occurrence point.
With the specifying method shown in FIG. 8, it is necessary to start a new OAM session individually for each of the fractionated MEGs. This causes complication in the management for setting each session. Further, each of the sessions transmits/receives the OAM frame by each MEG without synchronizing with each other, so that the measurement time in each MEG is not necessarily consistent. Thus, there are cases where there is no same phenomenon occurred even when the measurement results of each session are collated. In such case, it is difficult to specify the occurrence point.
The technique depicted in Patent Document 1 is designed to overcome such issue. However, with this technique, it is necessary to execute a series of processing such as “discriminate the OAM frame→acquire the latest reception counter value→write the acquired reception counter value to the OAM frame→transmit the OAM frame” for the received OAM frame in each of the relay devices existing on the transmission path.
FIG. 9 is an explanatory chart showing an example where the frame transmission order is inverted in the relay device existing in the middle of MEG on the transmission path, which is the packet loss ratio measurement method depicted in Non-Patent Document 1 shown in FIG. 6 to FIG. 8. A thick-line arrow shows the OAM frame, and a thin-line arrow shows the user frame, respectively.
With the LM protocol, a strict order characteristic is required between the user frame and the OAM frame. When there is an inversion of the transmission order occurred as shown in FIG. 9, the counter value contained in the OAM frame becomes invalid, so that an accurate packet loss ratio cannot be calculated.
Therefore, the technique which requires actions for adding new data by processing the OAM frame in the relay device in the middle of the transmission path such as the technique depicted in Patent Document 1 has a risk of causing inversion of the transmission order as shown in FIG. 9. That is, such action for adding new data needs to be executed at a same speed as that of the regular data frame (user frame) transfer. Thus, a high performance is required for the hardware and software which execute that processing.
Further, when new data is added to the OAM frame in the relay device in the middle of the transmission path, the band of the OAM frame itself is increased thereby. Particularly, when transmission is done via multiple stages of relay devices, new data is to be added every time when going through the relay device. Thus, the band is increased greatly. In accordance with the increase in the band, a new frame loss is to be generated.
Therefore, when applying such technique, it is necessary to take a measure such as predicting in advance the increase in the band generated according to the measurement of the packet loss ratio and restricting the band of the user frame coming in from MEP in the measurement section, for example.
All the techniques depicted in Patent Documents 2 to 4 add new data to the data that is being transmitted as in the technique of Patent Document 1. That is, none of the techniques depicted in Patent Documents 1 to 4 can overcome the above-described issue. It is the same even when those techniques are combined.
The object of the present invention is to provide a transmission system, a transmission device, a packet loss ratio measurement method, and a packet loss ratio measurement program, which are capable of measuring the packet loss ratio between arbitrary devices on a transmission path without increasing the band of the OAM frame.